This invention relates generally to methods of modifying the growth of plant roots and specifically to methods of improving the harvestability or accessibility of plant roots by growth in proximity to a hydrophilic non-porous membrane or a hydrophobic porous membrane.
Much time and effort has been invested in modifying the growth of many plant species in order to increase ease of harvesting of, or access to, commercially valuable products (fruit, seeds, flowers, leaves, etc) but less effort has been made, and even less success achieved, with respect to the modification of plant root growth. In fact, the structure of a plant""s roots can be of great commercial interest; for example, because the roots themselves are a commercial product (or source thereof) or because their structure will greatly affect the ease of harvesting a plant or the ease and chances of success at uprooting and replanting the plant.
Examples of commercially valuable roots include bulk agricultural crops such as carrots or beetroot, etc and also roots grown for their pharmaceutical or homeopathic properties. The processing required after extraction of commercially valuable roots will vary greatly depending upon their intended use; for example, simple removal of most adhered growing medium for carrots; or intensive cleaning, chopping, heat treatment and chemical extraction for pharmaceutically valuable roots. In all cases, however, the ease of removing as much of the root system from the ground as possible and then separating the root system from the growth medium is important, both in terms of volume of root recovery and in post extraction processing costs.
When plants are being grown in bulk before replanting, for example seedlings in a nursery, it is again important to be able to remove as high a proportion as possible of the developing root system from the growth medium without damage, so that the replanted plant will have the best chance of regrowth whilst avoiding diseases caused by microbial attack on broken roots.
A further category of roots that are commercially valuable are those that release commercially valuable materials into the growing medium; for example, it is now known that most plant root systems release specific materials (e.g., antimicrobial materials, growth regulating materials including natural herbicides, etc) although often in very small amounts. Means of improving the growth of such root systems and particularly means of improving the collection of such exuded materials would be of great benefit.
Numerous materials that allow the passage of water whilst restricting the passage of suspended or even dissolved materials are known. One recently identified group of materials are hydrophilic polymers. Membranes of these materials are known to be impervious to liquid water but to allow the passage of water vapor (a process known as pervaporation). If there is a vapor pressure across a hydrophilic membrane, water will be absorbed in the form of vapor from the side with higher vapor pressure, and transported across the membrane and released as water vapor on the side with lower vapor pressure; the released water vapor may be used directly or condensed back to liquid water. However, in either case, it may be pure (both chemically and microbiologically) as any contaminants will be retained either on the other side of the membrane or (in some cases) in the membrane itself.
Hydrophobic porous membranes will also selectively allow the passage of water whilst retaining dissolved or suspended matter.
It has now been found that if plant roots are grown in proximity to certain membranes (i.e. hydrophilic non-porous or hydrophobic porous membranes) from which water is released the structure of the roots will be modified so that they are easier to harvest and/or to separate from the growth medium following harvesting. It has also been found that plant roots grown in proximity to such membranes from which water is released will tolerate growth in more confined volumes than is usual and will therefore be less likely to become pot bound.
There is therefore provided a method of modifying the growth of plant roots by growing the roots in proximity to a membrane from which water is released during the growth of the roots, wherein the membrane is a hydrophobic porous membrane or a hydrophilic non-porous membrane.
There is also provided a method of collecting materials exuded from plant roots by growing the plant roots in a growing medium that is surrounded by a membrane such that moisture is released into the growing medium from the membrane whilst materials exuded from the plant roots are retained within the growing medium by the membrane, wherein the membrane is a hydrophobic porous membrane or a hydrophilic non-porous membrane.